One of the methods of outputting images such as documents, graphic representations, or the like generated by personal computers or the like onto recording mediums such as sheets of paper, OHP films, or the like is known as an ink jet recording process.
In the ink jet recording process, an ink in the form of a solution is ejected from a nozzle toward a recording medium by a drive source which employs an electric field, heat, pressure, or the like for thereby forming an image on the recording medium. The ink jet recording process is advantageous in that it produces a low level of noise, requires a low running cost, can form images on sheets of ordinary paper, and does not discharge a waste material such as ink ribbons. Therefore, ink jet recording apparatus have been finding widespread use in recent years as recording apparatus for office or personal use.
The ink jet recording process is, however, disadvantageous in that images formed on recording media by this process have poor fixability properties, particularly water resistance and light resistance.
The reasons for such poor fixability properties are as follows: Generally, an ink for use in ink jet recording is composed of a water-soluble dye. For printing using such an ink, the ink is ejected toward a recording medium, and after the ink has been dried, its water-soluble dye remains on the recording medium and is held thereon by the van der Waals forces or hydrogen bonding for thereby fixing an image to the recording medium. Therefore, when a solvent such as water or the like which has a large affinity for the water-soluble dye is supplied to the recorded image, the dye is eluted, causing the image to blur.
The dye also moves, causing the image to blur, when the water-soluble dye which forms the image on the recording medium is supplied with thermal or light energy that is large enough to cancel out the van der Waals forces or hydrogen bonding between the dye and the recording medium. Furthermore, upon exposure of the dye which forms the image to light such as ultraviolet radiation or the like, the molecules of the dye itself are destroyed, causing the image to be faded, discolored, or lowered in density. Therefore, images formed by the dye are also of low light resistance.
The water resistance of images formed according to the ink jet recording process can be improved by using a recording medium of sized paper or a recording medium coated with a resin. The resin to be coated on the recording medium comprises a hydrophilic resin for allowing an image to be formed by a water-soluble dye. Attempts have also been made to improve the light resistance of images formed according to the ink Jet recording process by selecting a dye having a certain basic skeleton or introducing a certain substituent group into a side chain of dye molecules thereby to limit the molecular structure of the dye.
If the recording medium of sized paper is used to improve the water resistance of images formed according to the ink jet recording process, then it takes a long time to fix the ink to the recording medium as the recording medium has low ink absorption.
If the recording medium coated with a hydrophilic resin is used, then it has good ink absorption, but tends to form ink dots of large diameter or ink dots having blurred edges. Since the resin coated on the recording medium is hydrophilic, it essentially is not sufficiently effective to improve the water resistance of recorded images. Another problem of the recording medium coated with a hydrophilic resin is that it impairs the basic advantage of the ink jet recording process that sheets of ordinary paper can be used as the recording medium.
The attempts to limit the molecular structure of the dye for improved light resistance have not yet been sufficiently effective.
The present invention has been made to solve the above problems of the prior art.
It is an object of the present invention to form images of high water and light resistance on sheets of ordinary paper according to an ink jet recording process.